RASP News:
(Latest 5 news items)
July 1:
Cloud composite plot change:
The "Cumulus Cloudbase for Cu Potential > 0" was often missing small
regions where the Cu potential was in fact greater than zero.
That has now been altered to "raster" plotting, which will ensure that
all locations with a positive Cu potential will be displayed.
Dec 10, 2005:
Plot "frame" change:
RASP plots contain a dashed line "frame" indicating an outer zone of
decreased confidence resulting from mismatches between the coarse and
fine nested grids near the boundary. A recent WRF model
alteration doubled the width of the smoothed zone near the boundary so
the "frame" border has been increased to reflect that change.
Nov 6:
Cloud Parameter Changes:
I've altered the cloud parameters by removing the previous
"OvercastDevelopment" parameters and replacing them with forecasts for
"Extensive CloudBase" and "BL Cloud Cover". "Extensive
CloudBase" is a replacement for "OvercastDevelopment", based on a
model-predicted cloud water prediction. "BL Cloud Cover" is
based upon the relative humidity in the BL and while overly simplistic
can still be useful.
Nov 2:
World-wide accuracy improvement:
Finally - after beating my head against mysteries with few clues for
the past three days, I figured how to to uncompress the new "GRIB2"
files produced by NCEP's GFS (Global Forecast System), allowing use of
GFS predictions at 0.5x0.5 degree resolution (about 50km) to
initialize the non-US forecasts (I've been using GRIB1 files with
100km resolution). So I've now changed to their use for the
SW_SOUTHAFRICA and GREATBRITAIN runs, which should result in improved
accuracy of larger-scale (non-terrain-generated) features such as the
position/movement of fronts and upper-level clouds.
Oct 30:
Meteorological model updated:
Today I upgraded my WRF meteorological model to the latest version
available, which has several bug fixes and in particular should reduce
boundary matching problems (which are occasionally apparent in the
region between the domain boundary and the dashed-line "frame").
After correcting some problems I believe I now have it working
properly, but will keep an closer-than-usual eye on the processing for
the next day.
View ALL recent news items here
ARCHIVE of
older news items which have now lost much relevance
I only look at the webpages and maps that I use personally or that I
suspect might contain an error. If you notice a consistent
problem with a webpage or map, please post a message on the
RASP Forum.
Links to Further Information:
RASP UniViewer
- displays BLIPMAPs for the current day at multiple times
RASP Archive Viewer
- displays BLIPMAPs for the current and previous days (one time per day only)
Parameter descriptions
BASIC thermal forecast parameters
- a short and simple list of the parameters most important for thermal soaring
July 2002 SOARING magazine BLIPMAP article - a descriptive "first thing to read" for potential BLIPMAP users, giving an
overview of BLIPMAP predictions
Additional information
but intended for users
of my traditional RUC and ETA BLIPMAPs, not these RASP BLIPMAPs, so
allowances must be made
Overview
These forecasts are intended to help the
meteorology-minded pilot better evaluate soaring conditions. The
maps are particulalry useful to cross-country soaring pilots, since
they allow evaluation of conditions away from the home field.
Utilizing the forecasts can require some self-education (though that
can't be too hard since over 2000 US pilots actively use BLIPMAPs in
the US) as individualized assistance is not provided. At first
glance the website can seem intimidating since so many parameters are
forecast - but most are "supplemental" forecasts to be used as needed
and many users normally look only at the three or four they have found
to be most useful, such as the expected lift strength or the maximum
(dry) thermalling height or cloud potential/height forecasts, looking
at additional parameters only under special conditions.
How are these RASP forecasts produced ?
My traditional RUC and ETA BLIPMAP forecasts are
obtained by post-processing forecast files output from NCEP prognostic
models, so horizontal and vertical resolution is determined by that
used in those models. Here I am instead running a prognostic
model myself, so am able to specify the vertical/horizontal grid
(though of course subject to limits of practicality). A WRF
(Weather Research and Forecasting) model is being initialized and
marched forward in time at 180 second time intervals to produce
forecasts at 3 hr increments. Initial and boundary conditions
come from the larger-scale models run by NCEP, in this case from the
GFS model having a resolution of around 100km. To increase
accuracy, forecasts are produced for three different grids: a
large-domain coarse-mesh grid (36 km), a 12 km grid nested inside it,
and a small-scale fine-mesh 4km grid within that (but only results for
the latter two grids are presented). Since the data needed to
make such runs is available globally, the forecasts can be made for
anywhere in the world.
Notes and Caveats:
The Future ?
() One is not supposed to believe all the details of these
forecasts, particularly since the smallest-scale structure is constantly
changing yet one a few snapshots at different times are shown.
Rather, one should be looking for patterns.
() Forecasts for points close to the boundary will be less
accurate than for those located nearer the center of the domain, due
to inevitable mis-matchings between the coarse and fine grids.
In particular, predictions of max/min BL vertical velocity are very
noisy and inaccurate near the boundary (particularly where boundary
condition problems exist). To remind users of this, a dotted
line marks the "frame" outside of which coarse-fine boundary
interaction problems are most prevalent.
() The "Explicit CloudWater Cloudbase" estimates are based on
cloud water predicted from internal model equations and problematical since
there is no simple criterion for differentiating "mist" concentrations
from "cloud" concentrations. The criterion presently used is a
first guess.
() The "Cu Potential" and "Sfc. LCL" predictions are based on a simple formula which considers
only water vapor at the surface
() This model does not ingest as much observational data as do the institutional models
such as RUC and ETA, hence some effects are not included.
() The fact that these forecasts are only a snapshot in time of
a fairly noisy field should be particularly emphasized for the 4 km
resolution forecasts, as forecasts for, say, 30 minutes before or
after would look different. At this point it's difficult to
figure how much value they really add anything, but one never knows til
one tries.
() The "Vert. Velocity at 850mb (or 700mb or 500mb)" and
"Vert. Velocity Slice at Vert.Vel.Max" parameters attempt to forecast
mt. wave events, although strong vertical velocities resulting from
deep BL convergence can also be found in the plots. The first
parameter gives a plan view of vertical velocity at the 850mb level, a
height of roughly 1500 m MSL and thus often above the BL top.
The second parameter is a vertical slice taken at a point of maximum
vertical velocity (as found at a height of approximately 1500 m AGL
within a horizontal box which excludes ane outer edge of the domain;
the position of that slice is indicated by a dotted line on the plot
of the first parameter (with left-right on the slice always being
left-right on the plan view). A label above the plots gives the
location and magnitude of the found maximum value. Mt. wave
predictions are best made using resultions no larger than 4km, since a
coarser grid generally does not resolve the waves accurately.
() Time loops are provided to illustrate the variability, and hence uncertainty,
over a 3 hour period. Unfortunately the color scales are not identical for all maps
in the loop, but generally they are roughly comparable.
If these forecasts prove useful, I would plan to
make the code public so that others might produce high-resolution
soaring forecasts for their own local regions. Such a
"distributed computing" concept is much more practical than trying to
have a centralized computational effort (whereas the RUC/ETA BLIPMAP
processing is only practical when done centrally since for them the
very large "native grid" files must be downloaded, vice the much
smaller files tha RASP downloads). What is required is a DSL
connection, a reasonably powerful Linux computer, and time and energy
and commitment. The forecast images could be uploaded to either
a club's webpages or to a special section of the DrJack website for
viewing by others.
